border-1px($color)
  position: relative
  &:after
     display: block
     position: absolute
     left: 0
     bottom: 0
     width: 100%
     border-top: 1px solid $color
     content: ' '

border-none()
  &:after
    display: none

bg-image($url)
  background-image: url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3), (min-device-pixel-ratio: 3)
    background-image:  url($url + "@3x.png")
